Polymer films made of certain hydroxyl functional copolymers are well known for their gas barrier properties. For example, a copolymer of ethylene and vinyl alcohol may be extruded into a film that is resistant to the flow of gases such as oxygen. Such films find use in, for example, the food packaging industry to prevent spoilage of perishable produce.
The gas barrier material may also be used to form a pressurized bladder or cushioning device for applications such as in footwear. In this application, the gas barrier layer may be alternated in the membrane with a second layer made of an elastomeric material. Bonk et al. in U.S. Pat. No. 6,127,026 describe such a membrane comprising a microlayer polymeric composite having at least about 10 microlayers. The microlayers alternate between at least one gas barrier material and at least one elastomeric material, exemplified by thermoplastic polyurethane (TPU).
To conserve natural resources, it is desirable to recycle and reuse composites containing such barrier layers and elastomeric materials. For example, to recycle the composite of Bonk et al. U.S. Pat. No. 6,127,026, it is possible to grind the composite to obtain a mixture containing both the gas barrier layer material and the thermoplastic polyurethane.
In addition, it is known to use blends of TPU and copolymers of ethylene and vinyl alcohol (EVOH) to produce coextruded sheets for a variety of uses related to gas barriers. For example, Bonk et al in U.S. Pat. No. 6,203,868 describe membranes including a barrier layer made of a blend of one or more thermoplastic polyurethanes and one or more copolymers of ethylene and vinyl alcohol.
Making blends of TPU and EVOH may involve regrinding composites such as described above or coextruding blends of thermoplastic polyurethane and barrier polymer at elevated temperature. When such components are ground and coextruded, a gel is observed to form in the mixture that deleteriously affects flow properties, handleability, and appearance of the extruded layer. In particular, the formation of gel leads to a hazy appearance in the coextruded layer. For cosmetic purposes, and to improve the handleability of coextruded blends of thermoplastic polyurethane and hydroxyl functional polymers such as ethylene vinyl alcohol copolymer, it would be desirable to reduce the gel content of the coextruded sheets prepared from the blend of TPU and hydroxyl functional polymer.